This revised R01 application is in response to the recent Program Announcement (PA-04-152): MDMA: Research Areas Needing More Emphasis. Its purpose is to study use of ecstasy (MDMA) in youth. With over 10 million people in the United States having used ecstasy at least once in their lives and majority of them being youth, there is an urgent need to understand the patterns and risk and protective factors associated with its use to be able to provide adequate prevention and intervention to this population. The proposed project is a secondary analysis of (1) data from a 7-year (1999-2005) series of annual surveys from the National Survey on Drug Use and Health (NSDUH, formerly called the National Household Survey on Drug Abuse (NHSDA)) and (2) the National Survey of Parents and Youth (NSPY), a longitudinal survey of youth and their parents on their substance use, and attitudes, beliefs and intentions towards substance use, and risk factors. Study aims: (1) To describe trends in ecstasy use from 1999 to 2005 in youth; to examine if the trends differ by gender, ethnicity and geographic area; to examine the effects of national policies on ecstasy use and on trends of ecstasy use in youth: (2) To examine ecstasy use in relation to use of other substances in youth. (3) To assess the relationship of ecstasy use with emotional and behavioral problems, as well as suicidal behaviors in youth, controlling for use of other drugs; to examine if the patterns of the relationships differ by gender; and (4) To assess risk and protective factors (at the individual level, family level, and community level) for ecstasy use in youth. To identify factors uniquely associated with ecstasy use and those shared with use of other substances. It is hoped that the findings of this project will help us to better understand patterns of ecstasy use, as well as risk and protective factors, and point the way to more specific research with clinical and policy relevance in this important field.